Active-matrix display devices employ thin-film transistors (TFTs) used as the switching elements of pixels. Further, thin-film transistors are used also for switching elements of drivers formed in a frame area (non-displaying area) located on an outer side of an active area (display area).
Moreover, for these TFTs, a TFT of a double-channel structure type has been proposed, which aims to increase the on-state current. A TFT of this type comprises a first amorphous silicon film, a second amorphous silicon film located above the first amorphous silicon film so as to oppose the first amorphous silicon film, and a gate electrode interposed between the first amorphous silicon film and the second amorphous silicon film. That is, the TFT includes two amorphous silicon films. Further, with the above-described structure, the occupying area of the TFT can be reduced as compared to the case where the first amorphous silicon film and the second amorphous silicon film are formed in layers of the same level.